Sputtering target having an annular vault

ABSTRACT

A target for a magnetron plasma sputter reactor. The target has an annular vault facing the wafer to be sputter coated and has a width of preferably at least 5 cm and an aspect ratio of at least 1:2, preferably 1:1. Various types of magnetic means positioned around the walls of the vault, some of which may rotate along the vault, create a magnetic field in the vault to support a plasma extending over a large volume of the vault from its top to its bottom. The large plasma volume within the vault increases the probability that the sputtered metal atoms will become ionized and be accelerated towards an electrically biased wafer support electrode.

RELATED APPLICATIONS

This application is a division of Ser. No. 09/703,601, filed Nov. 1,2000 pending, which is a continuation in part of Ser. No. 09/518,180,filed Mar. 2, 2000, now issued as U.S. Pat. No. 6,277,249, which is acontinuation in part of Ser. No. 09/490,026, filed Jan. 21, 2000, nowissued as U.S. Pat. No. 6,251,242.

FIELD OF THE INVENTION

The invention relates generally to plasma sputtering. In particular, theinvention relates to the sputter target and associated magnetron used ina sputter reactor and to an integrated via filling process usingsputtering.

BACKGROUND ART

A semiconductor integrated circuit contains many layers of differentmaterials usually classified according to whether the layer is asemiconductor, a dielectric (electrical insulator) or metal. However,some materials such as barrier materials, for example, TiN, are not soeasily classified. The two principal current means of depositing metalsand barrier materials are sputtering, also referred to as physical vapordeposition (PVD), and chemical vapor deposition (CVD). Of the two,sputtering has the inherent advantages of low cost source material andhigh deposition rates. However, sputtering has an inherent disadvantagewhen a material needs to be filled into a deep narrow hole, that is, onehaving a high aspect ratio. The same disadvantage obtains when a thinlayer of the material needs to be coated onto the sides of the hole,which is often required for barrier materials. Aspect ratios of 3:1present challenges, 5:1 becomes difficult, 8:1 is becoming arequirement, and 10:1 and greater are expected in the future. Sputteringitself is fundamentally a nearly isotropic process producing ballisticsputter particles which do not easily reach the bottom of deep narrowholes. On the other hand, CVD tends to be a conformal process equallyeffective at the bottom of holes and on exposed top planar surfaces.

Up until the recent past, aluminum has been the metal of choice for themetallization used in horizontal interconnects and in the viasconnecting two levels of metallization. In more recent technology,copper vias extend between two levels of horizontal copperinterconnects. Contacts to the underlying silicon present a largerproblem, but may still be accomplished with either aluminum or copper.Copper interconnects are used to reduce signal delay in advanced ULSIcircuits. It is understood that copper may be pure copper or a copperalloy containing up to 10% alloying with other elements such asmagnesium and aluminum. Due to continued downward scaling of thecritical dimensions of microcircuits, critical electrical parameters ofintegrated circuits, such as contact and via resistances, have becomemore difficult to achieve. In addition, due to the smaller dimensions,the aspect ratios of inter-metal features such as contacts and vias arealso increasing. An advantage of copper is that it may be quickly andinexpensively deposited by electrochemical processes, such aselectroplating. However, sputtering or possibly CVD of thin copperlayers onto the walls of via holes is still considered necessary to actas an electrode for electroplating or as a seed layer for theelectroplated copper. The discussion of copper processes will be delayeduntil later.

The conventional sputter reactor has a planar target in parallelopposition to the wafer being sputter deposited. A negative DC voltageis applied to the target of magnitude sufficient to ionize the argonworking gas into a plasma. The positive argon ions are attracted to thenegatively charged target with sufficient energy to sputter atoms of thetarget material. Some of the sputtered atoms strike the wafer and form asputter coating thereon. Most usually, a magnetron is positioned in backof the target to create a larger magnetic field adjacent to the target.The magnetic field traps electrons, and, to maintain charge neutralityin the plasma, the ion density also increases. As a result, the plasmadensity and sputter rate are increased. The conventional magnetrongenerates a magnetic field lying principally parallel to the target.

Much effort has been expended to allow sputtering to effectively coatmetals and barrier materials deep into narrow holes. High-density plasma(HDP) sputtering has been developed in which the argon working gas isexcited into a high-density plasma, which is defined as a plasma havingan ionization density of at least 10¹¹ cm⁻³ across the entire space theplasma fills except the plasma sheath. Typically, an HDP sputter reactoruses an RF power source connected to an inductive coil adjacent to theplasma region to generate the high-density plasma. The high argon iondensity causes a significant fraction of sputtered atoms to be ionized.If the pedestal electrode supporting the wafer being sputter coated isnegatively electrically biased, the ionized sputter particles (metalions) are accelerated toward the wafer to form a directional column thatreaches deeply into narrow holes.

HDP sputter reactors, however, have disadvantages. They involve asomewhat new technology and are relatively expensive. Furthermore, thequality of the sputtered films they produce is often not the best,typically having an undulatory surface. Also, high-energy ions,particularly the argon ions which are also attracted to the wafer, tendto damage the material already deposited.

Another sputtering technology, referred to as self-ionized plasma (SIP)sputtering, has been developed to fill deep holes. See, for example,U.S. patent application Ser. No. 09/373,097 filed Aug. 12, 1999 by Funow U.S. Pat. No. 6,183,614 and U.S. Patent Application filed Oct. 8,1999 by Chiang et al. Both of these patent applications are incorporatedby reference in their entireties. In its original implementations, SIPrelies upon a somewhat standard capacitively coupled plasma sputterreactor having a planar target in parallel opposition to the wafer beingsputter coated and a magnetron positioned in back of the target toincrease the plasma density and hence the sputtering rate. The SIPtechnology, however, is characterized by a high target power density, asmall magnetron, and a magnetron having an outer magnetic pole pieceenclosing an inner magnetic pole piece with the outer pole piece havinga significantly higher total magnetic flux than the inner pole piece. Insome implementations, the target is separated from the wafer by a largedistance to effect long-throw sputtering, which enhances collimatedsputtering. The asymmetric magnetic pole pieces causes the magneticfield to have a significant vertical component extending far towards thewafer, thus enhancing and extending the high-density plasma volume andpromoting transport of ionized sputter particles.

The SIP technology was originally developed for sustainedself-sputtering (SSS) in which a sufficiently high number of sputterparticles are ionized that they may be used to further sputter thetarget and no argon working gas is required. Of the metals commonly usedin semiconductor fabrication, only copper has a sufficiently highself-sputtering yield to allow sustained self-sputtering.

The extremely low pressures and relatively high ionization fractionsassociated with SSS are advantageous for filling deep holes with copper.However, it was quickly realized that the SIP technology could beadvantageously applied to the sputtering of aluminum and other metalsand even to copper sputtering at moderate pressures. SIP sputteringproduces high quality films exhibiting high hole filling factorsregardless of the material being sputtered.

Nonetheless, SIP has some disadvantages. The small area of the magnetronmay require circumferential scanning of the magnetron in a rotary motionat the back of the target to achieve even a minimal level of uniformity,and even with rotary scanning, radial uniformity is difficult toachieve. Furthermore, very high target powers have been required in thepreviously known versions of SIP. High-capacity power supplies areexpensive and necessitate complicated target cooling. Lastly, knownversions of SIP tend to produce a relatively low ionization fraction ofsputter particles, for example, 20%. The remaining non-ionized fractionof sputtered particles has a relatively isotropic distribution ratherthan forming a forward directed column which results from metal ionsbeing accelerated toward a biased wafer. Also, the target diameter in atypical commercial sputter reactor is only slightly greater than thewafer diameter. As a result, those holes being coated located at theedge of the wafer have radially outer sidewalls which see a largerfraction of the target and are more heavily coated than the radiallyinner sidewalls. Therefore, the sidewalls of the edge holes areasymmetrically coated.

Other sputter geometries have been developed which increase theionization density. One example is a multi-pole hollow cathode target,several variants of which are disclosed by Barnes et al. in U.S. Pat.No. 5,178,739. Its target has a hollow cylindrical shape, usually closedwith a circular back wall, and is electrically biased. Typically, aseries of magnets, positioned on the sides of the cylindrical cathode ofalternating magnetic polarization, create a magnetic field extendinggenerally parallel to the cylindrical sidewall.

Another approach uses a pair of facing targets facing the lateral sidesof the plasma space above the wafer. Such systems are described, forexample, by Kitamoto et al. in “Compact sputtering apparatus fordepositing Co—Cr alloy thin films in magnetic disks,” Proceedings: TheFourth International Symposium on Sputtering & Plasma Processes,Kanazawa, Japan, Jun. 4-6, 1997, pp. 519-522, by Yamazato et al. in“Preparation of TiN thin films by facing targets magnetron sputtering,ibid., pp. 635-638, and by Musil et al. in “Unbalanced magnetrons andnew sputtering systems with enhanced plasma ionization,” Journal ofVacuum Science and Technology A, vol. 9, no. May 3, 1991, pp. 1171-1177.The facing pair geometry has the disadvantage that the magnets arestationary and create a horizontally extending field that is inherentlynon-uniform with respect to the wafer.

Musil et al., ibid., pp.1174, 1175 describe a coil-driven magneticmirror magnetron having a central post of one magnetic polarization andsurrounding rim of another polarization. An annular vault-shaped targetis placed between the post and rim. This structure has the disadvantagethat the soft magnetic material forming the two poles, particularly thecentral spindle, are exposed to the plasma during sputtering andinevitably contaminate the sputtered layer. Furthermore, the coil driveprovides a substantially cylindrical geometry, which may not be desiredin some situations. Also, the disclosure illustrates a relativelyshallow geometry for the target vault, which does not take advantage ofsome possible beneficial effects for a concavely shaped target.

Helmer et al. in U.S. Pat. No. 5,482,611 describe a target having anannular groove or vault facing the substrate. Stationary magnets arearranged on the outside of the vault sidewalls with parallel magneticpolarities so as to create a magnetic field generally parallel to thevault walls within the vault and having a magnetic cusp or null spotnear the opening of the vault. The magnetic cusp directs the metalsputter ions in a beam towards the wafer. However, Helmer et al. admitthat uniformity of deposition with this magnetic configuration is notgood. Lantsman in U.S. Pat. No. 5,589,041 discloses an plasma etchchamber having a dielectric roof that is formed with a vault so as toshape the plasma.

It is thus desired to combine many of the good benefits of the differentplasma sputter reactors described above while avoiding their separatedisadvantages.

Returning now to copper processing and the structures that need to beformed for copper vias, as is well known to those in the art, in atypical copper interconnect process flow, a thin barrier layer is firstdeposited onto the walls of the via hole prior to the copper deposition.The barrier layer prevents copper from diffusing into the insulatingdielectric layer separating the two copper levels and also to preventintra metal and inter metal electrical shorts. A typical barrier forcopper over silicon oxide includes Ta or TaN or a combination thereof,but other materials have been proposed, such as W/WN and Ti/TiN amongothers. In a typical barrier deposition process, the barrier layer isdeposited using PVD or other method to form a continuous layer betweenthe underlying and overlying copper layers including the contact area atthe bottom of the via hole. Thin layers of these barrier materials havea small but finite transverse resistance. A structure resulting fromthis copper interconnect process produces a contact having a finitecharacteristic resistance (known in the art as a contact or viaresistance) that depends on the geometry. Conventionally, the barrierlayer at the bottom of the contact or via hole contributes about 30% ofthe total contact or via resistance. Geffken et al. disclose in U.S.Pat. No. 5,985,762 a separate directional etching step to remove thebarrier layer from the bottom of the via hole over an underlying copperfeature but not from the via sidewalls so that, during the sputterremoval of the copper oxide at the via bottom, the dielectric is notpoisoned by the sputtered copper. This process requires presumably aseparate etching chamber. Furthermore, the process deleteriously alsoremoves the barrier at the bottom of the trench in a dual-damascenestructure. They accordingly deposit another conformal barrier layer,which remains under the metallized via.

As a result, there is a need in the art for a method and apparatus toform a low-resistance contact between underlying and overlying copperlayers and having a low contact resistance without unduly complicatingthe process.

A copper layer used to form an interconnect is conveniently deposited byelectrochemical deposition, for example, electroplating. As is wellknown, an adhesion or seed layer of copper is usually required tonucleate an ensuing electrochemical deposition on the dielectricsidewalls as well as to provide a current path for the electroplating.In a typical deposition process, the copper seed layer is depositedusing PVD or CVD methods, and the seed layer is typically deposited ontop of the barrier layer. A typical barrier/seed layer depositionsequence also requires a pre-clean step to remove native oxide and othercontaminants that reside on the underlying metal that has beenpreviously exposed in etching the via hole. The pre-clean step, forexample, a sputter etch clean step using an argon plasma, is typicallyperformed in a process chamber that is separate from the PVD chamberused to deposit the barrier and seed layers. With shrinking dimension ofthe integrated circuits, the efficacy of the pre-clean step, as well assidewall coverage of the seed layer within the contact/via feature,become more problematical.

As a result, the art needs a method and apparatus that improves thepre-clean and deposition of the seed layer. Further, the seed layerneeds to be conformally deposited in all portions of the via hole evenif the barrier layer is removed in portions of the hole.

SUMMARY OF THE INVENTION

The invention includes a magnetron producing a large volume or thicknessof a plasma, preferably a high-density plasma. The long travel paththrough the plasma volume allows a large fraction of the sputtered atomsto be ionized so that their energy and directionality can be controlledby substrate biasing.

The target may be formed with more than one annular vault on the sidefacing the substrate. Each vault should have a width of at least 2.5 cm,preferably at least 5 cm, and more preferably at least 7 cm and shouldhave an aspect ratio of at least 1:2, preferably at least 1:1. The widthis thus at least 10 times and preferably at least 25 times the darkspace, thereby allowing the plasma sheath to conform to the vaultoutline.

In one embodiment of the invention, the target includes at least oneannular vault on the front side of the target. The backside of thetarget includes a central well enclosed by the vault and accommodatingan inner magnetic pole of one polarity. The backside of the target alsoincludes an outer annular space surrounding the vault and accommodatingan outer magnetic pole of a second polarity. The outer magnetic pole maybe annular or be a circular segment which is rotated about the innermagnetic pole.

In one embodiment, the magnetization of the two poles may beaccomplished with soft pole pieces projecting into the central well andthe outer annular space and magnetically coupled to magnets disposedgenerally behind the well and outer annular space. In a secondembodiment, the two poles may be radially directed magnetic directions.In a third embodiment, a magnetic coil drives a yoke having a spindleand rim shape.

In one advantageous aspect of the invention, the target covers both thespindle and the rim of the yoke as well as forming the vault, therebyeliminating any yoke sputtering.

According to another aspect of the invention, the relative amount ofsputtering of the top wall of the inverted vault relative to thesidewalls may be controlled by increasing the magnetic flux in the areaof the top wall. An increase of magnetic flux at the sidewalls mayresult in a predominantly radial distribution of magnetic field betweenthe two sidewalls, resulting in large sputtering of the sidewalls.

One approach for increasing the sputtering of the top wall placesadditional magnets above the top wall with magnetic polarities alignedwith the magnets just outside of the vault sidewalls. Another approachuses only the top wall magnets to the exclusion of the sidewall magnets.In this approach, the back of the target can be planar with noindentations for the central well or the exterior of the vaultsidewalls. In yet another approach, vertical magnets are positioned nearthe bottom of the vault sidewalls with vertical magnetic polaritiesopposed to those the corresponding magnets near the top of the vaultsidewalls, thereby creating semi-toroidal fields near the bottomsidewalls. Such fields can be adjusted either for sputtering or forprimarily extending the top wall plasma toward the bottom of the vaultand repelling its electrons from the sidewalls. A yet further approachscans over a top wall a small, closed magnetron having a centralmagnetic pole of one polarity and a surrounding magnetic pole of theother polarity.

Various magnetron configurations are possible for use with the vaultedtarget. A particularly advantageous design includes an annular innersidewall magnet of one polarity, an outer sidewall magnet of the otherpolarity, and a roof magnet that rotates about the central axis. Theroof magnet may be composed of an annular outer magnet of the secondpolarity surrounding an inner magnet of the first polarity. The innersidewall magnet is preferably divided into two axial portions separatedby a non-magnetic spacer, thereby smoothing the erosion pattern on theinner target sidewall because the magnetic field is curved towards thenon-magnetic; however, although the non-magnetic spacer is not requiredfor all aspects of the invention.

The invention also includes a two-step sputtering process, the firstproducing high-energy ionized copper sputter ions, the second producinga more neutral, lower-energy sputter flux. The two-step process can becombined with an integrated copper fill process in which the first stepprovides high sidewall coverage and may break through the bottom barrierlayer and clean the copper. The second step completes the seed layer.Thereafter, copper is electrochemically deposited in the hole. Forsputtering into a dual-damascene structure, the conditions arepreferably set so that the first step sputters the barrier from thebottom of the via hole but not from the more accessible trench floor.

After forming a first level of metal on a wafer and pattern etching asingle or dual damascene structure for a second level of metal on thewafer, the wafer is processed in a PVD cluster tool to deposit a barrierlayer and a seed layer for the second metal level.

Instead of using a pre-clean step (for example, a sputter etch cleaningstep), in accordance with one aspect of the present invention, asimultaneous clean-deposition step (i.e., a self-clean deposition step)is carried out. The inventive self clean deposition is carried out usinga PVD deposition chamber that is capable of producing high-energyionized target material. In accordance with one embodiment of thepresent invention, the high-energy ions physically remove material onflat areas of a wafer. In addition, the high-energy ions can dislodgematerial from a barrier layer disposed at the bottom of a contact/viafeature. Further, in accordance with one embodiment of the presentinvention, wherein an initial thickness of the barrier layer is small,the high-energy ions can remove enough material from the barrier layerto provide direct contact between a seed layer and the underlying metal(for example, between a copper underlying layer and a copper seedlayer). In addition to providing direct contact between the two copperlayers, the inventive sputtering process also causes redeposition ofcopper over sidewalls of the contact/via to reinforce the thickness ofthe copper seed layer on the sidewall. This provides an improved pathfor current conduction, and advantageously improves the conformality ofa layer subsequently deposited by electroplating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a first embodiment of amagnetron sputter reactor of the invention using a stationary,circularly symmetric magnetron.

FIG. 2 is a schematic cross-sectional diagram illustrating thecollimating function of the target of the invention.

FIG. 3 is a schematic cross-sectional view of a second embodiment of amagnetron sputter reactor of the invention using a rotating, segmentedmagnetron with vertically magnetized magnets.

FIG. 4 is a schematic cross-sectional view of a third embodiment of amagnetron sputter reactor of the invention using a rotating, segmentedmagnetron with radially magnetized magnets.

FIG. 5 is a schematic cross-sectional view of a fourth embodiment of amagnetron sputter reactor of the invention using an electromagneticcoil.

FIG. 6 is a cross-sectional view of a fifth embodiment of a magnetron ofthe invention using additional magnets at the roof of the vault toincrease the roof sputtering.

FIG. 7 is a cross-sectional view of a sixth embodiment of a magnetron ofthe invention using only the vault magnets.

FIG. 8 is a cross-sectional view of a seventh embodiment of a magnetronof the invention using additional confinement magnets at the bottomsidewall of the vault.

FIG. 9 is a cross-sectional view of an eighth embodiment of a magnetronof the invention using a closed magnetron over the vault roof andseparate magnets for the vault sidewalls.

FIGS. 10-12 are cross-sectional views of ninth through eleventhembodiments of magnetrons of the invention.

FIGS. 13 and 14 are respectively a cross-sectional view and a schematicplan view of a twelfth embodiment of the invention using stationaryouter sidewall magnets and rotating inner sidewall magnets.

FIG. 15 is a schematic plan view of a variant of the twelfth embodiment.

FIG. 16 is a cross-sectional view of the target and magnetron of thetwelfth embodiment illustrating the resultant magnetic field.

FIG. 17 is a graph of sputtering yield as a function of copper ionenergy.

FIGS. 18 and 19 are cross-sectional views illustrating the effects ofhigh-energy ionized sputter deposition, particularly the effect of ahigh-energy copper PVD deposition removing the barrier layer at thebottom of the via.

FIG. 20 is a cross-sectional view illustrating how one copper PVDreactor can be used to both remove the barrier at the via bottom and todeposit a copper layer in its place.

FIG. 21 is a sectioned orthographic view of a desired barrier layer in adual-damascene interconnect.

FIGS. 22 and 23 are cross-sectional views of a desirable structure for abarrier layer and copper seed layer in a dual-damascene interconnect.

FIG. 24 is a flow diagram of a process usable for achieving the desiredinterconnects of FIGS. 20 and 23 including a electroplating via fill.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention uses a complexly shaped sputter target and a speciallyshaped magnetron which have the combined effect of impressing a magneticfield producing a thick region of relatively high plasma density. As aresult, a large fraction of the metal atoms sputtered from the targetcan be ionized as they pass through the plasma region. Sputtered metalions can be advantageously controlled by substrate biasing to coat thewalls of a deep, narrow hole and to selectively interact with thealready deposited barrier layer dependent upon the local geometry.

The inventive apparatus has been used to achieve several novel processesinvolving selective removal of layers at the bottom of high aspect-ratioholes and the selective sputter deposition on areas dependent upon theirgeometries. Multi-step processes involving both removal and depositioncan be performed in the same sputter reactor, for example, the inventivereactor with a novel target and associated magnetron.

Apparatus

A magnetron sputter reactor 10 of a first embodiment of the invention isillustrated in the schematic cross-sectional view of FIG. 1. It includesspecially shaped sputter target 12 and magnetron 14 symmetricallyarranged about a central axis 16 in a reactor otherwise described forthe most part by Chiang et al. in the above referenced patentapplication. This reactor and associated processes will be referred toas SIP⁺ sputtering in contrast to the SIP sputter reactor of Chiang etal., which uses a planar target. The shaped target 12 or at least itsinterior surface is composed of the material to be sputter deposited.The invention is particularly useful for sputtering copper, but it maybe applied to other sputtering materials as well. It is understood thattarget may be composed of alloys, typically to less than 10% ofalloying. For example, copper is often alloyed with silicon, aluminum,or magnesium. As is known, reactive sputtering of materials like TiN andTaN can be accomplished by using a Ti or Ta target and including gaseousnitrogen in the plasma. Other combinations of metal targets and reactivegases are possible.

The target 12 includes an annularly shaped downwardly facing vault 18opposed to a wafer 20 being sputter coated. The vault 18 couldalternatively be characterized as an inverted annular trough or moat.The vault 18 has an aspect ratio of its depth to radial width of atleast 0.5:1 and preferably at least 1:1. The tested embodiment had avault width of 7.5 cm and an aspect ratio of 1.4:1. The vault 18 has ancylindrical outer sidewall 22 outside of the periphery of the wafer 20,a cylindrical inner sidewall 24 overlying the wafer 20, and a generallyflat, annular vault top wall or roof 25 (which extends across the spacebetween the annular sidewalls 22, 24 and closes the bottom of thedownwardly facing vault 18). The sidewalls 20, 22 in this embodimentextend generally parallel to the central axis 16, and the roof 25extends generally perpendicularly. The target 12 also includes a centralportion forming a spindle 26 including the inner sidewall 24 and agenerally planar face 28 spanning the space formed at the bottomterminus of the inner sidewall 24 in parallel opposition to the wafer20. The target 12 is continuous across its parts 22, 25, 24, 28 with nostructure intervening between these parts and the process space betweenthe target 12 and the wafer 20. The target 12 also includes a flange 29which extends radially outwardly from near the terminus of the outersidewall 22 and which is vacuum sealed to the lower chamber body of thesputter reactor 10.

The magnetron 14 of the embodiment illustrated in FIG. 1 includes one ormore central magnets 30 having a first vertical magnetic polarity andone or more outer magnets 32 of a second vertical magnetic polarityopposite the first polarity and arranged in an annular pattern. That is,one is N-S; the other, S-N. In this embodiment the magnets 30, 32 arepermanent magnets, that is, composed of strongly ferromagnetic materialand are stationary. The inner magnets 30 are radially disposed within oraxially upward of a cylindrical central well 36 formed in the spindle 26and between the opposed portions of the inner target sidewall 24 whilethe outer magnets 32 are disposed generally radially outside of theouter target sidewall 22. A circular magnetic yoke 34 magneticallycouples tops of the inner and outer magnets 30, 32. The yoke is composedof a magnetically soft material, for example, a paramagnetic material,such as SS410 stainless steel, that can be magnetized to thereby form amagnetic circuit for the magnetism produced by the permanent magnets 30,32. Permanently magnetized yokes are possible but are difficult toobtain in a circular geometry.

A cylindrical inner pole piece 40 of a similarly magnetically softmaterial abuts the lower ends of the inner magnets 30 and extends deepwithin the target well 36 adjacent to the inner target sidewall 24 toproduce, in this case, a N pole within the well 36. (It is of courseappreciated that the selection of an N or S pole is for the most partarbitrary because almost all practical magnetic effects depend only uponthe relative polarities of different poles.) If the magnetron 14 isgenerally circularly symmetric, it is not necessary to rotate it foruniformity of sputter deposition. A tubular outer pole piece 42 of amagnetically soft material abuts the lower end of the outer magnets 32and extends downwardly outside of the outer target sidewall 22. Themagnetic pole pieces 40, 42 of FIG. 1 differ from the usual pole facesin that they and the magnets 30, 32 are configured and sized to emit amagnetic field B in the target vault 18 that is largely perpendicular tothe magnetic field of the corresponding associated magnets 30, 32. Inparticular, the magnetic field B is generally perpendicular to thetarget vault sidewalls 22, 24.

This configuration has several advantages. First, the electrons trappedby the magnetic field B, although gyrating about the field lines,otherwise travel generally horizontally and radially with respect to thetarget central axis 16. Plasma sheaths are formed on both vaultsidewalls 22, 24 which reflect electrons traveling along the magneticfield lines toward the vault sidewalls. As a result, the electrons aresubstantially bound within the vault 18, and electron loss is minimized,thus increasing the plasma density. Secondly, the vertical depth of themagnetic field B intensifying the plasma density is determined by theheight of the target sidewalls 22, 24. This depth can be considerablygreater than that of a high-density plasma region created by magnets inback of a planar target. As a result, sputtered atoms traverse a largerregion of a high-density plasma and are accordingly more likely tobecome ionized. The support structure for the magnetron 14 and its partsis not illustrated but can be easily designed by the ordinary mechanic.The support structure usually includes an overlying cover shielding andsupporting the magnetron.

The remainder of the sputter reactor 10 is similar to that described byChiang et al. in the above referenced patent application although ashort-throw rather than a long-throw configuration may be used. Longthrow is defined by Chiang et al. as the separation between the targetand wafer as being at least 80% and preferably at least 140% of thewafer diameter. The target 12 is vacuum sealed to a grounded vacuumchamber body 50 through a dielectric target isolator 52. The wafer 20 isclamped to a heater pedestal electrode 54 by, for example, a clamp ring56 although electrostatic chucking is possible. An electrically groundedshield 58 acts as an anode with respect to the cathode target 12, whichis negatively biased by a variable DC power supply 60. DC magnetronsputtering is conventional in commercial applications, but RF sputteringcan enjoy the advantages of the target and magnetron of the inventionand is especially advantageous for sputtering non-metallic targets. Anelectrically floating shield 62 is supported on the electricallygrounded shield 58 or chamber 50 through a dielectric shield isolator64. An annular cylindrical knob 66 extending downwardly from the outertarget sidewall 22 and positioned inwardly of the uppermost part of thefloating shield 62 protects the upper portion of the floating shield 62and the target isolator 52 from being sputter deposited from the strongplasma disposed within and slightly vertically outwardly of the targetvault 18. The gap between the upper portion of the floating shield 62and the target knob 66 and flange 29 is small enough to act as a darkspace preventing the plasma from propagating into the gap.

A working gas such as argon is supplied into the chamber from a gassource 68 through a mass flow controller 70. A vacuum pumping system 72maintains the chamber at a reduced pressure, typically a base pressurein the neighborhood of 10⁻⁸ Torr. Although a floating pedestal electrode54 can develop a desired negative self-bias, it is typical in highplasma-density sputtering for an RF power supply 74 to RF bias thepedestal electrode 54 through an isolation capacitor, which results in acontrolled negative DC self-bias. A controller 76 regulates the powersupplies 60, 74, mass flow controller 70, and vacuum system 72 accordingto a sputtering recipe prerecorded in it with recordable magnetic oroptical media.

The structures of the target and magnetron have several advantages. Asmentioned previously, secondary electrons are largely trapped within thevault 18 with little loss even upon collision with the target sidewalls22, 24, more specifically reflected from the plasma sheaths adjacent thesidewalls. Also, the plasma thickness is relatively large, determined bythe sidewall heights, thereby increasing the ionization fraction of thesputtered target atoms. The separation of the inner and outer poles 40,42 is relatively small, thereby increasing the magnetic field intensitywithin the vault 18. The target 12 is continuous across the pole pieces40, 42, thus preventing the magnetic material of the poles from beingsputtered and deposited on the semiconductor wafer 20.

The relatively high ionization fraction allows this fraction of thesputtered target atoms to have their trajectories toward the wafer becontrolled both by the magnetic field looping from the target toward thewafer and by the electric field induced by the DC self-bias applied tothe pedestal. Increasing the DC self-bias draws the ions into highaspect-ratio holes, thereby allowing high bottom and sidewall coverageof such high aspect-ratio holes. On the other hand, the ionizationfraction is less than 100%, and the remaining sputtered atoms areneutral. In some situations a finite neutral component is useful, andthe ratio of neutrals to ions can be controlled by adjusting powerlevels and chamber pressures.

The high aspect ratio of the vault 18 also improves the symmetricfilling of holes located near the edge of the wafer, particularly inconfigurations having a shorter throw than that illustrated in FIG. 1.As schematically illustrated in FIG. 2, a hole 78 located at the rightedge of the wafer 20 is to have a conformal layer sputter deposited onits sides. The size of the hole 78 and the thickness of the wafer 20 aregreatly exaggerated, but the geometry remains approximately valid. If aplanar target were being used, the right side of the wafer hole 78 wouldsee a much larger fraction of the target than the left side and wouldthus be coated with a commensurately thicker layer. However, with thevault-shaped target 12, the hole 78 sees neither the inner sidewall 24of the left side of the vault 18 nor the left vault top wall 25. Eventhe upper portion of the outer sidewall 22 of the left side of the vault18 is shielded from the wafer hole 78 by the inner sidewall 24 of theleft side of the vault 18. As a result, the two sidewalls of the hole 78to be coated see areas of the vault-shaped target that are much closerin size than for a planar target, and the sidewall coating symmetry isthereby greatly increased.

The target structure, as a result, can provide sputtered particleshaving trajectories preferentially aligned perpendicularly to the wafersurface, but without an apertured collimator, which tends to becomeclogged with sputtered material. The effect is increased by a highaspect ratio for the vault, preferably at least 1:2, and more preferablyat least 1:1. The tested target had a vault with an aspect ratio of1.4:1.

A sputter reactor 80 of second embodiment of the invention isillustrated in the schematic cross-sectional view of FIG. 3. A magnetron82 includes the previously described inner magnets 30 and inner polepiece 40. However, one or more outer magnets 84 and an outer pole piece86 extend around only a segment of the circumference of the target, forexample between 15° and 90°. An asymmetric magnetic yoke 88 shaped as asector magnetically couples the inner and outer magnets 30, 84 but onlyon the side of target well 36 toward the outer magnets 84. In fact, acircular yoke 88, although larger, would not affect the operativemagnetic field. As a result, a high-density plasma is generated in onlya small circumferential portion of the target vault 18. For self-ionizedplating (SIP) and particularly sustained self-sputtering (SSS), a highplasma density is desired. In view of the limited capacity of realisticpower supplies 60, the high plasma density can be achieved by reducingthe volume of the magnetron 82.

To achieve uniform sputtering, a motor 90 is supported on the chamberbody 50 through a cylindrical sidewall 92 and roof 94 preferablyelectrically isolated from the biased target flange 29. The motor 90 hasa motor shaft connected to the yoke 88 at the target axis 16 and rotatesthe magnetron 82 about that axis 16 at a few hundred rpm. Mechanicalcounterbalancing may be provided to reduce vibration in the rotation ofthe axially offset magnetron 82. The mechanical details are notaccurately represented in FIG. 3 but will be described more completelybelow.

Other magnet configurations are possible to produce similar magneticfield distributions. A sputter reactor 100 of a third embodiment of theinvention is illustrated in the schematic cross-sectional view of FIG. 4A magnetron 102 includes an inner magnet 104 having a magnetizationdirection generally aligned with a radius of the target 12 about thetarget axis 16. One or more outer magnets 106 are similarly radiallymagnetized but anti-parallel to the magnetization of the inner magnet104 with respect to the center of the vault 18. A C-shaped magnetic yokehas two arms 110, 112 in back of and supporting the respective magnets104, 106 and a connector 114 supported on and rotated by the shaft ofthe motor 90.

The magnets 104, 106 may be advantageously positioned only on reducedcircumferential portions of the sidewalls 24, 22 of the target vault 18so as to concentrate the magnetic field there. Furthermore, in thisconfiguration extending along only a small segment of the targetperiphery, the magnets 104, 106 may be conveniently formed of platemagnets.

Electromagnetic coils may replace the permanent magnets of thepreviously described embodiments. A sputter reactor 120 of a fourthembodiment of the invention is illustrated in the schematiccross-sectional view of FIG. 5. A magnetron 122 includes a magnetic yokeincluding a central spindle 124 fit into the well 36 of the target 12and a tubular rim 126 surrounding the outer sidewall 24 of the targetvault 18. The magnetic yoke also includes a generally circular backpiece 128 magnetically coupling the spindle 124 and the rim 126. Anelectromagnetic coil 130 is wound around the spindle 124 below the backpiece 128 and inside of the rim 126. The coil 130 is preferably poweredby a DC electrical source but a low-frequency AC source can be used. Thecoil 130 in conjunction with the magnetic yoke creates a generallyradial magnetic field in the target vault 18.

The previously described embodiments have emphasized sputtering thevault sidewalls 22, 24 preferentially to sputtering the vault top wallor roof 25 (see FIG. 1) since relatively few of the magnetic field linesterminate on the vault roof 25. The metal ionization fraction can beincreased if sputtering is increased in the vault roof 25 since theplasma thickness experienced by the average sputtered atom is increased.Also, the directionality of sputtered material leaving the vault 18 isincreased.

The increased roof sputtering can be achieved in a number of ways. In afifth embodiment of a magnetron 140 illustrated in cross-section in FIG.6 with the remainder of the sputtering chamber being similar to theparts illustrated in FIG. 3. A target 142 is similar to the previouslydescribed target 12 except for a thinner roof portion 144. Similarly tothe magnetron 82 of FIG. 3, it includes the rotatable yoke 88 supportingthe inner magnets 30 of a first vertical polarity magnetically coupledto the inner pole piece 40 and the outer magnets 84 of a second verticalpolarity magnetically coupled to the outer pole piece 86. These magnets30, 84 and pole pieces 40, 86 produce a generally radial magnetic fieldB extending between the sidewalls 22, 24 of the vault 18. The magnetron82 additionally supports on the magnetic yoke 88 an inner roof magnet146 of the first vertical polarization aligned with the inner magnets 30and an outer roof magnet 148 of the second vertical polarization alignedwith the outer magnets 86. The opposed roof magnets 146, 148magnetically coupled by the yoke 88 produce a semi-toroidal magneticfield B penetrating the vault roof 144 at two locations. Thereby,electrons are trapped along the semi-toroidal magnetic field andincrease the plasma density near the vault roof 144, thereby increasingthe sputtering of the vault roof 144.

In the illustrated embodiment, the outer magnets 84 and outer pole piece86 occupy only a segment of the periphery of the target 142 but arerotated along that periphery by the motor 90. Similarly, inner and outerroof magnets 146, 148 extend only along a corresponding segment angle.However, a corresponding non-rotating magnetron can be created by makingthe roof magnets 146, 148, outer magnet 84, and outer pole piece 86 inannular shapes. The same circularly symmetric modification may be madeto the embodiments described below.

The roof sputtering can be further emphasized by a sixth embodiment of amagnetron 150, illustrated in FIG. 7, which includes the inner and outerroof magnets 146, 148 but which in the illustrated embodiment includesneither the inner magnets within the well 36 nor the outer magnetsoutside of the outer sidewall 22. This configuration produces arelatively strong semi-toroidal magnetic field B adjacent to the vaultroof 144 and a weaker magnetic field B in the body of the vault 18adjacent to the sidewalls 22, 24. Therefore, there will be much moresputtering of the roof 144 than of the sidewalls 22, 24. Nonetheless,magnetic field lines in the vault body terminate at the sidewalls 22,24, thereby decreasing electron loss out of the plasma. Hence, themagnetic field intensity may be low in the vault, but the plasma densityis still kept relatively high there so that the target atoms sputteredfrom the roof 144 still traverse a thick plasma region and areaccordingly efficiently ionized.

Since no magnets or pole pieces are placed in the target well 36 oroutside of the outer target sidewall 22 and assuming the target materialis non-magnetic, the inner and outer sidewalls 24, 22 may be increasedin thickness even to the point that there is no well and no appreciablevolume between the outer sidewall 22 and the chamber wall. That is, theback of the target 142 may have a substantially planar face 152, 154,156. However, the inventive design of this embodiment still differs froma target having a circularly corrugated surface in that the spacing ofthe opposed roof magnets 146, 148 is at least half of the radial vaultdimension and preferably closer to unity. This is in contrast to theembodiments of FIGS. 1, 3, and 4 in which the two sets of magnets areseparated preferably by between about 100% and 150% of the vault width.Alternatively stated, the width of the vault 18 in the radial directionshould be at least 2.5 cm, preferably at least 5 cm, and most preferablyat least 10 cm. These dimensions, combined with the vault aspect ratiobeing at least 1:2 assures that the vault width is at least 10 times andpreferably at least 25 times the plasma dark space, thus guaranteeingthat the plasma conforms to the shape of the vault 18. These vaultwidths are easily accommodated in a sputter reactor sized for a 200 mmwafer. For larger wafers, more complex target shapes become even easierto implement.

A seventh embodiment of a magnetron 160 illustrated in thecross-sectional view of FIG. 8 includes the inner and outer main magnets30, 84, although they are preferably somewhat shorter and do not extendbelow the vault roof 144. The magnetron also includes the inner andouter roof magnets 146, 148. However, neither the inner pole piece northe outer pole piece needs to be used to couple the magnetic field fromthe main magnets 30, 84 into the vault 18. Instead, all these magnetsproduce a horizontally oriented semi-toroidal field B adjacent the vaultroof 144. Some of these magnets may be eliminated as long as there areopposed magnets associated with the inner and outer target sidewalls 22,24. Instead of ferromagnetic or paramagnetic pole pieces, non-magnetic(e.g. aluminum or hard stainless steel) or even diamagnetic spacers 162,164 are supported below the inner and outer main magnets 30, 84respectively. Henceforth, non-magnetic materials will be assumed toinclude diamagnetic materials unless specifically stated otherwise. Theinner spacer 162 supports on its lower end an inner sidewall magnet 166of the second magnetic polarity, that is, opposite that of itsassociated main inner magnet 30. Similarly, the outer spacer 164supports on its lower end an outer sidewall magnet 168 of the firstmagnetic polarity, that is, opposite that of its associated main outermagnet 84. Both the sidewall magnets 166, 168 are located near thebottom of the respective vault sidewalls 24, 22. Because, they havepolarities opposed to those of their associated main magnets 30, 84 theycreate two generally vertically extending semi-toroidal magnetic fieldsB′ and B″ near the bottom of the vault sidewalls 24, 22. Because oftheir opposed magnetic orientations, the sidewall magnets 166, 168create two anti-parallel components of radial magnetic field across thevault 18. However, because of the relative spacings of the poles, thesemi-toroidal magnetic fields B′ and B″ dominate.

In one sub-embodiment, the horizontally extending magnetic field B nearthe vault roof 144 is much stronger than the vertically extendingmagnetic fields B′ and B″ near the vault sidewalls 24, 22. As a result,sputtering of the roof 144 predominates. Alternatively, increasedsidewall fields B′ and B″ can increase the amount of sidewall sputteringin a controlled way. In any case, the vertically extending sidewallfields B′ and B″ are sufficient to support a plasma throughout much ofthe body of the vault 18. Also, the sidewall fields B′ and B″ areoriented to repel electrons in the plasma flux from the roof 144,thereby decreasing the electron loss of that plasma.

All of the previous embodiments have used magnets that extend generallyalong either the entire circumference or a segment of the circumferenceof various radii of the target. However, an eighth embodiment of amagnetron 170 illustrated in the cross-section view of FIG. 9 treats theplanar vault roof 144 distinctly differently than the band-shaped vaultsidewalls 22, 24. The sidewall magnetic assembly is similar to that ofFIG. 6 and includes the rotatable yoke 88 supporting the inner magnets30 of a first vertical polarization magnetically coupled to the innerpole piece 40 and the segmented outer magnets 84 of an opposed secondvertical polarization magnetically coupled to the outer pole piece.These produce a generally radially directed magnetic field B across thevault 18. The rotating magnetic yoke 88 also supports a closed magnetronover the vault roof 144 including an inner magnet 172 of one verticalmagnetic polarization and a surrounding outer magnet 174 of the othervertical magnetic polarization producing between them a cusp-shapedmagnetic field B′ adjacent the vault roof 144. In the simplestsub-embodiment, the inner magnet 172 is cylindrical, and the outermagnet 174 is annular or tubular, surrounds the inner magnet 172,thereby producing a circularly symmetric cusp field B′. However, othershapes are possible, such as a radially or circumferentially alignedracetrack or a pair of nested segment-shaped magnets. The roof magnetronof FIG. 9 is the general type of magnetron described by Fu and by Chianget al. in the previously referenced patent applications for SIPsputtering of a planar target, and those references provide guidance onthe design of such a closed unbalanced magnetron having a strong outerpole surrounding a weaker inner pole of the opposite polarity.

The figure does not adequately illustrate the magnetic yoke 88 which inthe conceptually simplest implementation would magnetically isolate theroof magnets 172, 174 from the sidewall magnets 30, 84 while stillmagnetically coupling together the roof magnets 172, 174 and separatelycoupling together the sidewall magnets 30, 84. However, in view of thelarge number of magnets, a more complex magnetic circuit can beenvisioned.

As has been shown in the cited patent applications, such a small closedroof magnetron will be very effective in highly ionized sputtering ofthe target roof 144. The sidewall magnets 30, 84 on the other hand willextend the plasma region down the height of the sidewalls 22, 24 as wellas cause a degree of sidewall sputtering depending on the relativemagnetic intensities.

The relative magnetic polarizations of roof magnets 172, 174 relative tothose of the sidewall magnets 30, 84 may be varied. Also, the sidewallmagnets 30, 84 and particularly the outer sidewall magnet 84 may be madefully annular so as to close on themselves so that optionally they donot need to be rotated and may be coupled by their own stationary yokewhile the roof magnets 172, 174 do rotate about the circular planar areaon the back of the vault roof 144 and are coupled by their rotating ownyoke.

Other combinations of the closed roof magnetron and the sidewall magnetsof other embodiments are possible.

A ninth embodiment of a magnetron 180 of the invention is illustrated inthe cross-sectional view of FIG. 10 and includes the inner and outermagnets 172, 174 overlying the vault roof 144. Side magnets 182, 184disposed outside of the vault sidewalls 142 have opposed verticalmagnetic polarities but they are largely decoupled from the roof magnets172, 174 because they are supported on the magnetic yoke 88 bynon-magnetic supports 186, 188. As a result, the side magnets 182, 184create a magnetic field B in the vault 18 that has two generallyanti-parallel components extending radially across the vault 18 as wellas two components extending generally parallel to the vault sidewalls.Thus, the magnetic field B extends over a substantial depth of the vault18 and further repels electrons from the sidewalls. In the illustratedembodiment, all the side magnets 182, 184 are segmented and rotate withthe roof magnets 172, 174. However, a mechanically simpler design formsthe side magnets 182, 184 in annular shapes and leaves one or both ofthem stationary. As illustrated, the polarities are such that the toppole of the inner side magnet 182 has the same polarity as the bottompole of the adjacent annular top magnet 174 while the outer side magnet184 has the opposite relationship with the annular top magnet 174.However, these polarities may be varied.

A tenth embodiment 190 illustrated in the cross-sectional view of FIG.11 is similar to the magnetron 180 of FIG. 10 except that an inner sidemagnet 192 is smaller than the outer side magnet 184, thereby allowingtailoring of the magnetic fields on the two vault sidewalls. Theopposite size relationship is also possible.

An eleventh embodiment 200 illustrated in the cross-sectional view ofFIG. 12 dispenses with the top magnets and uses only the two sidemagnets 182, 184 which may be of the same size or of unequal size. Inthis case, the yoke 88 need not be magnetic.

A twelfth embodiment 210 illustrated in the cross-sectional side view ofFIG. 13 is the subject of U.S. patent application Ser. No. 09/703,738,filed on Nov. 11, 2000 by A. Subramani et al., incorporated herein byreference in its entirety. This embodiment has similar functionality tothat of FIG. 10 but has further capabilities.

The illustrated upper part of the sputtering chamber includes acylindrical wall composed of a bottom frame 212 and a top frame 214, onwhich is supported a chamber roof 216. The SIP⁺ vault-shaped target 12is fixed to the bottom frame 212. All these parts are sealed together toallow cooling water to circulate in a space 218 in back of the target12. The vault-shaped target 12 includes the annular vault 18 having theouter sidewall 22, the inner sidewall 24, and the vault roof 25, allgenerally circularly symmetric with respect to the vertical chamber axis16. The inner and outer vault sidewalls 22, 24 extend generally parallelto the chamber axis 16 while the vault roof 25 extends generallyperpendicularly thereto. That is, the vault 18 is annularly shaped witha generally rectangular cross section.

A magnetron 220 is placed in back of the vaulted target 12 in closeassociation with the vault 18. The magnetron 220 includes a stationaryring-shaped outer sidewall magnet assembly 222 placed outside the outervault sidewall 22 and having a first vertical magnetic polarity. Thepreferred structure for the outer sidewall magnets 224 is morecomplicated than that illustrated, as is described in the patentapplication to Subramani et al., but the functions remain much the same.A rotatable inner sidewall magnet assembly 224 includes an upper tubularmagnet 226 and a lower tubular magnet 228 separated by a non-magnetictubular spacer 230 having an axial length at least half the respectivelengths of the two tubular magnets 226, 228. The two tubular magnets226, 228 have a same second vertical magnetic polarity opposite that ofthe outer sidewall magnet 222. However, the non-magnetic spacer 230 isnot required, and other magnet configurations may be selected to achievea desired erosion pattern. The bottom of the lower tubular magnet 228 isseparated from the back of a central planar portion 232 of the vaultedtarget 12 by a small gap 234 having an axial extent of between 0.5 to1.5 mm.

The magnetron also includes a rotatable roof magnet assembly 236 in anested arrangement of an outer ring magnet 238, generally circularlyshaped, having the first magnetic polarity surrounding an inner rodmagnet 240 having the second magnetic polarity and a magnetic yoke 242supporting and magnetically coupling the magnets 238, 240. It ispreferred that the total magnetic flux of the outer ring magnet 238 besubstantially greater than that of the inner magnet 240, for example,having a ratio of at least 1.5. It is preferred, although not required,that the magnetic polarity of the outer ring magnet 238 be anti-parallelto that of the inner sidewall magnet 224 so as to avoid strong magneticfields adjacent to the inner upper corner of the target vault 18 andinstead to intensify the magnetic field at the outer upper comer, whichis being more quickly scanned. The metal ions produced in the veryhigh-density plasma adjacent the roof are focused by the sidewallmagnets 222, 224 into a column directed to the wafer.

Both the inner sidewall magnet 224 and the roof magnet assembly 236 arerotatable about the chamber axis 16. The inner sidewall magnet 224 isconnected to and supported by a shaft 244 rotated about the chamber axis16 by a motor 246. The magnetic yoke 242 supporting the roof magnets238, 240 is also fixed to the rotating shaft 244.

The motor shaft 244 and the inner sidewall magnet 224 includes an innerpassageway 250 configured for passage of cooling fluid, usually water,supplied from a chiller 252 through an inlet port 254 to a rotary union256 connected to the motor shaft 244. The cooling water flows from thebottom of the inner sidewall magnet 224 through the gap 234 at thebottom of the inner sidewall magnet 224. It then flows upwardly betweenthe inner vault sidewall 24 and the inner sidewall magnet 224. Therotating roof magnet assembly 236 stirs up the cooling water in the backof the target 12, thereby increasing its turbulence and coolingefficiency. The cooling water then flows down next to the outer vaultsidewall 22. As explained by Subramani et al., the tubular outersidewall magnet assembly 222 is composed of a large number of rodmagnets, and they are separated from the actual walls of the target 12.As a result, the cooling water can flow both through and below the outersidewall magnet 222 to one of several outlets 257 in the bottom frame212 and then through several risers 258 in the frames 212, 214 to anoutlet port 259 in the upper frame 214, whence the warmed cooling wateris returned to the chiller 252. This cooling design has the advantage ofsupplying the coldest water to the hottest, central portions of thetarget 12.

Even though the inner sidewall magnet 224 is rotating, its circularsymmetry causes it to produce the same magnetic field as that producedby a stationary cylindrical magnet. A schematic plan view of the magnetsis shown in FIG. 14. This figure is intended to represent the effectivemagnetic poles rather than actual magnets. The labeled polaritiescorrespond to the uppermost poles and do not necessarily reflect theeffective polarities within the vault 18. The inner sidewall magnet 224is included within the inner vault sidewall 24 and is essentiallycircularly symmetric even though it may be rotating. Similarly the outersidewall magnet 222 is positioned on the radial exterior of the outervault sidewall 22, and it also is substantially circularly symmetric.The roof magnet assembly 236 including the outer and inner roof magnets238, 240 is positioned over the vault roof between the outer and innersidewalls 22, 24, and it rotates about the center of the target. It isapparent that the roof magnet assembly 236 occupies less than 20% of thearea of the vault 18, and its effective magnetic fields occupy less than10%. These factors provide corresponding increases in effective targetpower densities. Nonetheless, circumferential scanning provides uniformsputtering of the target.

It is possible to increase the number of roof magnet assemblies. Forexample, as illustrated in the schematic plan view of FIG. 15, a secondroof magnet assembly 260 has outer and inner magnets 262, 264 of sizesand polarities matched to those of the first roof magnet assembly 236.The second roof magnet assembly 260 is disposed over the vault 18diametrically opposite the first roof magnet assembly 236 and is rotatedwith it. Additional roof magnet assemblies may be added. While themultiple roof magnet assemblies increase the sputtering rate,particularly of metal ions, they require additional power to achieve thesame peak plasma density.

The asymmetry between the roof magnet assembly 236 and the sidewallmagnets 222, 234 for the embodiment of FIGS. 13 and 14 producesdistinctly different magnetic field strengths and distributions indifferent parts of the vault 18, as is schematically illustrated in FIG.16. In the portion of the vault 18 with the roof magnet assembly 236,there is a strong magnetic field B adjacent the vault roof 25. With theillustrated magnetic polarities, the magnetic field is relatively weakerat the upper comer of the inner sidewall 24 but much stronger at theupper comer of the outer sidewall 22. The inclusion of the non-magneticspacer 230 between the two tubular magnets 226, 228 of the innersidewall magnet assembly 224 produces a magnetic field distribution thatis more parallel to the inner vault sidewall 24, thereby evening theerosion pattern there. In contrast, as illustrated on the left side, inportions of the vault 18 distant from the roof magnet assembly 236, themagnetic field B′ has a reduced intensity, particularly near the vaultroof 25. As a result, there is relatively more sputtering of the vaultroof 25 in areas of the roof magnet assembly 236 than elsewhere, and themetal ionization fraction in that portion is substantially higher. Incontrast, distant from the roof magnet assembly 236, there is relativelysubstantial sputtering of the vault sidewalls 22, 24 with an increasedfraction of neutral metal atoms being produced.

It is known that low-pressure sputtering requires a relatively highmagnetic field. It is thus possible to select chamber pressure andtarget power such that the plasma is supported only adjacent the roofmagnet assembly 236 or to select another combination of chamber pressureand target power such that the plasma is supported throughout the vault18.

It is thus seen that the complex geometry of the magnetron and target ofthe various embodiments of the invention provides additional controls onthe intensity, directionality, and uniformity of sputtering.

It is possible to include multiple concentric vaults and to associatemagnetic means with each of them.

It is also possible to additionally include an RF inductive coil toincrease the plasma density in the processing space between the targetand wafer. However, the unique configurations of the target andmagnetron of the invention in large part eliminate the need forexpensive coils.

Although the described embodiments have included a magnetron with avault having vertical sidewalls and producing a substantially horizontalmagnetic field in the vault. However, it is appreciated that themagnetic field cannot be completely controlled, and inclinations of themagnetic field may extend up to about 25°. Furthermore, the sidewallsmay form more of a V-shaped vault with sidewall slope angles of up to25°, but a maximum of 10° is preferred.

Although the invention has been described with respect to sputtering acoating substantially consisting of the material of the target, it canbe advantageously used as well for reactor sputtering in which a gassuch as nitrogen or oxygen is supplied into the chamber and reacts withthe target material on the wafer surface to form a nitride or an oxide.

Processes and Structures

The magnetron 180 of FIG. 12 using stationary annular side magnets hasbeen used in a number of experiments with sputtering copper and hasshown unusual capabilities. We believe that the unusual results arisefrom the enhanced ionization fraction of the sputtered copper as itpasses through the extended magnetic field in the vault and therestriction of the high-density plasma to only a portion of the vault.The copper ions can be attracted to the wafer by the inherent DCself-bias of a floating pedestal and the attraction can be increased byRF biasing the pedestal. The controlled attraction controls the energyand directionality of the copper ions incident on the wafer and deepinto the via hole and allows controlled fractions of ionized and neutralsputtered atoms.

The sputtering yield for copper ions as a function of the ion energy isplotted in FIG. 17. Thus, the higher sputter particles energies possiblewith the inventive magnetron and other magnetrons can produce a highcopper yield in the case that the underlying copper is exposed duringsputter processing by high-energy copper ions. Furthermore, the ratio ofsputtering yield of tantalum relative to copper is 1:4 and further lowerfor TaN, thereby providing selectivity over copper. The believed effectof high-energy sputtered copper is schematically illustrated in thecross-sectional view of FIG. 18. A substrate 270 is formed with a lowercopper metal feature 272. An inter-level dielectric layer 274 isdeposited thereover and photolithographically etched to form a via hole276. After pre-cleaning, a thin barrier layer 278 is substantiallyconformally coated in the via 276 hole and over the top of thedielectric 274. The subsequent high-energy copper ion sputter depositionand resultant resputtering of the copper already deposited on the waferreduces the deposition on the field area on the planar top of the oxide274 and at a bottom 280 of the via hole 276. However, the copper atomsresputtered from the bottom 280 of the via hole 276 is of lower energythan the incident copper ions and are emitted generally isotropically.As a result, they tend to coat the via sidewalls 282 even more than thevia bottom 280 because the sidewalls 282 are not exposed to theanisotropic high-energy copper ion column. The bottom sputtering furtheris likely to etch through the barrier layer 278 at the via bottom 280,thus exposing the underlying copper 272. Furthermore, the top layer ofthe copper 272 is cleaned in what is generally a PVD process. As aresult, as illustrated in FIG. 19, the barrier layer 278 is removed atthe bottom of the via hole 276 and a recess 284, experimentally observedto be concave, is formed in the underlying copper 272. Further,relatively thick copper sidewalls 286 of thickness d_(S) are depositedwhile a copper field layer 288 of thickness d_(B) is formed over theplanar top of the dielectric 274. Because of the high resputtering,overhangs do not form on the lip of the via 276. The sidewall coveraged_(S)/d_(B) is observed to be in the neighborhood of 50 to 60% for hightarget power and low chamber pressure. The result may be described asselective PVD.

The removal of the lower barrier layer has two implications. The contactresistance is reduced because the barrier material is removed in thedirect current path, specifically at the interface of the via metalbeing deposited with the underlying metal feature, and the copper of theupper-level metallization is in direct contact with the copper of thelower-level metallization, namely, the copper feature 272. Furthermore,in prior systems, a high resistivity oxide of the underlying metalneeded to be removed by a pre-metallization cleaning step. With theinvention, the pre-clean that was necessary for that function to cleanthe oxide or residue at the top of the underlying copper 272 prior todepositing the barrier or seed layer is no longer required to assuredirect contact between the two copper levels since the PVD step isitself removing the barrier and cleaning the underlying copper or othermetal layer. Pre-cleaning on the sidewalls and top of the dielectric ismuch less of a requirement and may in some circumstances be eliminated.

It is noted that the structure illustrated in FIG. 19 shows the removalof the barrier layer 278 on the horizontal bottom of the via hole 276but its barrier field portion 290 remaining in the field area on theplanar top of the dielectric layer 274. This is possible if the metalionization fraction is less than 100% so that a substantial number ofunaccelerated metal neutrals are sputtered onto the field area. Theneutrals, however, are shielded from reaching the via bottom. As aresult, the high-energy metal ions can sputter the barrier layer 278 atthe bottom of the via hole 276, but they are overcome by thelower-energy metal neutrals at the top, and there is a net deposition ofcopper and no barrier removal in the field area on top of the dielectriclayer 274. This result differs from the process disclosed by Geffken etal. in the above patent in which all horizontally extending barrierlayers are removed.

The sidewall coverage afforded by the high-energy ionized sputterdeposition is sufficient for use as a seed layer. It is believed thatabout 5 nm sidewall coverage is required in 3 μm-deep vias having an11:1 aspect ratio. However, the copper field coverage is reduced overthe conventional sputtering process and does not provide a sufficientelectrical path for the electroplating current. Therefore, a short, moreconventional copper sputter process may be used to complete the copperseed layer and eliminate any voids in it and to thicken the fieldcoverage. The more conventional sputtering produces not onlylower-energy copper ions but a larger fraction of neutral copper sputterparticles, which do not respond to wafer biasing. The two steps can bebalanced to provide a balance between bottom coverage, sidewallcoverage, and blanket thickness. That is, the conformality can betailored. The more conventional copper sputter could be performed in aseparate sputter reactor. However, in view of the small quantity ofcopper needed to complete the seed layer, the same reactor used for thehigh-energy sputtering can be adjusted to effect lower-energysputtering. To accomplish this second step, for example, the targetpower can be reduced to reduce the plasma density and metal ionizationfraction, the chamber pressure can be raised above 1 milliTorr,preferably about 1.5 milliTorr or higher, to reduce the wafer self-bias,thus reducing the ion energy, and to decrease the metal ionizationfraction, the RF pedestal bias power can be reduced to decrease theacceleration of ions toward the wafer, or a combination of the threechanges can be made between the two steps.

The structure of FIG. 19 is accomplished by producing a relatively highbut not very high copper ionization fraction. It is possible to performwithin a single sputter reactor a two-step copper PVD process in whichthe first step produces the structure of FIG. 19 and the second step isperformed with chamber parameters adjusted to reduce the copper ionenergy so that, as illustrated in the cross-sectional view of FIG. 20,the via bottom is coated with a second copper layer 292 covering allareas including a via bottom portion 294. Further, it is noted that thetwo-step copper PVD process can be advantageously used even in the casewhere the first step does not leave a barrier field layer 290 and afirst copper field layer 288 is not deposited. For single-leveldamascene, the field region is subjected to CMP, and these extra layersin the field region are not crucial.

Following the formation of the second copper layer 292, the via hole isfilled and overfilled by electro chemical plating of copper using thesecond copper layer 292 both as a seed layer and an electrode.Thereafter, the copper and typically the barrier layers exposed over thefield area are removed by chemical mechanical polishing.

Although the description above is directed to removing the barrier layerat the bottom of the via hole, a similar two-step process may be used toproduce a more conformal seed layer coating even if the bottom barrierlayer is not removed. The chamber parameters for the first step areadjusted to emphasize middle sidewall coverage with little or no bottomand/or field coverage. The chamber parameters are then changed for thesecond step to emphasize bottom, upper sidewall, and field coverage. Inmost cases, this means that there is a substantial fraction of energeticmetal ions in the first step and a larger fraction of neutrals relativeto energetic ions in the second step. The two-step process is superiorto a one-step process with intermediate chamber parameters because thelatter tend to immediately begin producing an overhanging lip at the topof the via hole which would interfere with bottom and middle sidewallcoverage.

The invention can be advantageously applied to more complex anddemanding structures desired in advanced integrated circuits. A dualdamascene structure is illustrated in the sectioned orthographic view ofFIG. 21, which allows inter-level vias and horizontal interconnects tobe metallized in a single metallization process. A generally dielectricunderlayer 300 includes a copper feature 302 in its surface that needsto be electrically contacted through an overlying inter-level dielectriclayer 304. A horizontally extending trench 306 is formed at the top ofinter-level dielectric layer 304, and one or more vias 308 (only one ofwhich is illustrated) are formed between the bottom of the trench 306and the corresponding ones of the copper features 302. A single sequenceof metallization steps are used to simultaneously metallize the trench306 (providing the horizontal interconnects) and the vias 308 to thelower-level metallization 302. However, a barrier layer 310 is requiredbetween the metal and any neighboring dielectric materials, for example,a TaN barrier for copper metallization. The barrier layer 310 is dividedinto a field portion 312 on top of the upper dielectric layer 304, atrench sidewall portion 314, a trench floor portion 316, and a viasidewall portion 318. All these portions 312, 314, 316, and 318 aredesired for a reliable integrated circuit. However, it is desired thatthe barrier layer 310 not extend over the bottom of the via hole 308 inorder to reduce the contact resistance to the metal feature.Accordingly, it is greatly desired that a sputtering process beavailable which has high bottom coverage in the trench 306 and no bottomcoverage in the via hole 308. The dual-damascene process disclosed byGeffken et al. in the above cited patent lacks this selectivity. It isnoted that the trench 306 has a very low aspect ratio along its axis butmay have a relatively high aspect ratio transverse to its axis. Chen etal. describe a somewhat similar selective removal and deposition in U.S.patent application Ser. No. 09/704,161, filed on Nov. 1, 2000 by L. Chenet al. incorporated herein by reference in its entirety. The grandparentapplication Ser. No. 09/518,180 now U.S. Pat. No. 6,277,249 discloses asimilar process to that discussed here with respect to FIGS. 14 and 15.

Such a selective removal of the barrier layer and selective depositionof copper is possible by adjusting the copper PVD process parameters toassure a balance between energetic copper ions and low-energy copperneutrals to produce the structure illustrated in cross section in FIG.22. A first copper seed layer 320 is deposited with relatively highcopper ion energy but a substantial neutral fraction so that the barrierlayer 310 at the bottom of the via hole 308 is removed and theunderlying copper feature 302 is cleaned. However, the copper layer 320is deposited over and thus protects the barrier layer 310 on the viasidewall 322, the trench floor 324, the trench sidewall 326, and thefield area 328 because these are either less exposed to the high-energycopper ions or more exposed to the lower-energy copper neutrals.

It is advantageous to perform the second copper seed deposition toproduce a conformal second copper seed layer 330, illustrated in thecross-sectional view of FIG. 23, to assure a thick sidewall and viabottom coverage as well as thick field coverage. The second copper seedlayer 330 is in direct contact with the cleaned upper surface of theunderlying copper feature 302, thus assuring a good electrical contact.

Following the deposition of the second copper seed layer 330, the viahole 308 and trench 306 are filled with copper by electrochemicalplating using the second copper layer 330 as both a seed layer and aplating electrode. Thereafter, chemical mechanical polishing removes anycopper exposed above the field area 328 outside of the trench 306 andtypically also the barrier layer 310 in the area.

For a given PVD chamber, particularly one of the SIP⁺ chamber describedabove, the metal ionization fraction is increased by operating at alower pressure or a higher target power. The metal ion energy can beincreased by these same two techniques or by increasing the pedestalself-bias by any technique.

It has been observed that the DC self-bias on a floating pedestaldepends on the chamber pressure. For example, at 0.85 milliTorr, a selfbias of about −20 VDC develops; and at 0.64 milliTorr, about −100 VDC.Thus, the chamber pressure can be used to control the copper ion energy.Similarly, increases of the target power from 20 kW to 40 kW show aboutthe same sequence of floating self-bias voltages, providing yet anothertool for copper ion energy.

An alternative approach to differentiate between the bottom and top ofthe via hole is to use an auxiliary electromagnetic coil wrapped aroundthe outside of the central axial portion of the chamber about itscentral axis to selectively generate an axial magnetic field between thetarget and wafer. When the field is turned on in the first step, themetal ions are preferentially guided toward the wafer compared to whenthe field is turned off or reduced in the second step. Wei disclosessuch an auxiliary electromagnet in U.S. patent application Ser. No.09/612,861, filed Jul. 10, 2000, now U.S. Pat. No. 6,352,629incorporated herein by reference in its entirety.

We believe that a sputter reactor such as those of FIGS. 11, 13, and 14having vaulted target and one or more nested top magnet assemblies andcontinuous inner and outer sidewall magnet can be operated in twodistinct modes determined by a combination of target power and chamberpressure. At higher power and lower pressure, the self-bias on thepedestal is between −100 to −150 VDC while at lower power and higherpressure, the self-bias assumes the more normal value of −30 VDC. Arelated difference is that, below a certain argon pressure, the targetvoltage is between about −450 and −700 VDC while above that pressure thetarget voltage drops to about −400 VDC. Although we are not bound by ourunderstanding of the invention, we believe that at lower pressure andhigher power the plasma is maintained in the vault only in the area ofthe top nested magnet assembly. Elsewhere, the plasma is extinguished.The magnetic fields in the area of the localized plasma may besufficient to funnel an ionized copper flux towards the wafer. Thecopper ionization fraction in this mode may be quite high, near 50%, andthe high wafer self-bias draws highly energetic ions to the wafer anddeep within high aspect-ratio holes. We believe that at higher pressurethe sidewall magnets are sufficient to maintain a plasma throughout theentire length of the vault. The lower plasma densities and increasedscattering produce a more neutral flux of copper atoms.

Applying RF bias to the pedestal through a coupling capacitor will alsoincrease the DC self-bias.

Some of the more pronounced high-energy sputtering results were obtainedwith a chamber pressure of 0.5 milliTorr, 40 kW of target power, and 300W of RF bias applied to the pedestal.

A process for accomplishing a copper via is illustrated in the flowdiagram of FIG. 24. In step 340, a inter-metal dielectric layer of, forexample, TEOS silicon dioxide or a low-k dielectric whether carbon-basedor silicon-based, is deposited, usually by a CVD process andphotolithographically patterned with via holes using a plasma etchingprocess. The dielectric patterning may be dual damascene, which includesboth the vias and interconnect trenches in a common connectingstructure. These steps are not directly part of the invention, and maybe practiced in any number of ways. It is assumed that the materialunderlying the via holes is copper. Contact holes to underlying siliconrequire a somewhat more complex process.

Thereafter, the wafer is placed in a multi-chamber integrated processingsystem. In some circumstances, no plasma preclean need be performed.Instead, one PVD system is used in step 342 to deposit the barrier layerinto the via hole and on top of the dielectric. Chemical vapordeposition (CVD) can instead be used for the barrier layer, or acombination of CVD and PVD can be used. In step 344, the high-energyionized copper deposition both cleans the bottom of the via hole andcoats its sidewalls, as has been described. This step also cleans theinterface of the underlying copper exposed beneath the barrier layer.Even in this mode, a substantial neutral flux is present that cannotpenetrate to the bottom of the via hole but does deposit on the planarfield portion above the dielectric. As a result, the barrier layer onthe field portion is not sputtered away by the energetic copper ions butis protected by some deposition of neutral copper.

In step 346, a lower-energy, more neutral copper sputter deposition isperformed to complete the seed layer, also used as the electroplatingelectrode. Whatever copper ions are present are accelerated by a lesserself-bias voltage and thus do not significantly sputter. Therefore, thelower energy copper ions the bottom of the via to provide bottomcoverage and the neutral copper effectively coats the exposed planarfield portion.

The two steps 344, 346 can be at least partially separated by requiringthe first step 344 to be performed at a pressure of less than 1.0milliTorr, more preferably 0.7 milliTorr or less, and most preferably0.5 milliTorr or less, while the second step 346 is performed at 1.5milliTorr or above.

By proper timing of the two steps 344, 346 and their associated targetpowers and chamber pressure, not only is the bottom barrier layerremoved but the conformality of the copper deposition at the via bottom,via sidewall, and field portion can be adjusted.

In step 348, the copper metallization is completed with anelectroplating or other electrochemical process.

Although this process has been described with reference to the inventivevault magnetron, similar high-energy ionized copper sputtering can beachieved in other ways. Achieving the desired selective PVD is believedto be eased by creating an energy distribution of the copper ions in theplasma with a peak energy of between 50 and 300 eV and/or by maintainingthe ratio of argon ions to copper ions Ar⁺/Cu⁺ in the plasma at 0.2 orless. Of course, the ultimate low fraction is obtained with sustainedself-sputtering. The low fraction of argon ions reduces the problemscommonly experienced with HDP sputtering.

Further, it has been shown the inventive SIP⁺ reactors can be used forthe sputter deposition of Ta, TaN, Al, Ti, and TiN and should be usablewith W, especially for the effects of selective removal, selectivedeposition, and a multi-step process.

The inventive process need not completely remove the barrier layer atthe bottom of the via to reduce the contact resistance. The outerportion, for example, of TiN while providing the barrier function hasthe highest resistivity. Hence, removing just the nitride portion wouldbe advantageous.

Of course, the invention can be used with copper alloyed with a fivepercent of an alloying element such as silicon, aluminum, or magnesium.Further, many aspects of the invention are applicable as well tosputtering other materials.

What is claimed is:
 1. A vault-shaped sputtering target, comprising acontinuous member having a vault annular about a central axis, having awidth of at least 5 cm, and disposed on a first side of said targethaving an annular inner sidewall, an opposed annular outer sidewall, atop wall, and an annular flange extending radially outwardly from saidouter sidewall, an aspect ratio of a depth of said vault to a width ofsaid vault being at least 1:2, said target being continuous within saidvault and in an area radially inwardly of said inner sidewall.
 2. Thetarget of claim 1, wherein said aspect ratio is at least 1:1.
 3. Thetarget of claim 1, wherein said continuous member additionally comprisesa planar face wall attached to said inner sidewall.
 4. The target ofclaim 3, wherein a well is formed by said inner sidewall and said planarface wall able to accommodate a magnet adjacent said inner sidewall. 5.The target of claim 1, wherein said continuous member additionallycomprises an annular projection extending from said flange away fromsaid outer sidewall and in alignment with said outer sidewall.
 6. Thetarget of claim 1, wherein said width is at least 7 cm.
 7. The target ofclaim 6, wherein said width is at least 10 cm.
 8. The target of claim 1,wherein said width is sized for a 200 mm wafer.
 9. The target of claim1, wherein said width is at least 25 times a dark space of a plasma. 10.The target of claim 1, wherein said target is a copper target.
 11. Thetarget of claim 1, wherein said target is a titanium target.
 12. Thetarget of claim 1, wherein said target is a tungsten target.
 13. Thetarget of claim 1, wherein said sidewalls extend parallel to each otherand perpendicular to at least a portion of said top wall.
 14. The targetof claim 1, wherein said annular flange is adapted to vacuum seal to aside portion of a sputtering reactor and to support said targetthereupon.
 15. The target of claim 1, wherein said annular flange isintegral with said outer sidewall.
 16. A vault-shaped sputtering target,comprising a continuous member having a vault annular about a centralaxis and disposed on a first side of said target having an annular innersidewall, an opposed annular outer sidewall, a top wall, an annularflange extending radially outwardly from said outer sidewall, and anannular projection extending away from said flange in an area of saidouter sidewall, an aspect ratio of a depth of said vault to a width ofsaid vault being at least 1:2, said target being continuous within saidvault and in an area radially inwardly of said inner sidewall.
 17. Thetarget of claim 16, wherein said continuous member additionallycomprises a planar face wall attached to said inner sidewall.
 18. Thetarget of claim 17, wherein a well is formed by said inner sidewall andsaid planar face wall able to accommodate a magnet adjacent said innersidewall.
 19. The target of claim 16, wherein said vault has a width ofat least 5 cm.
 20. The target of claim 19, wherein said vault has awidth of at least 7 cm.
 21. The target of claim 16, which is a coppertarget.
 22. The target of claim 16, wherein said annular flange isadapted to vacuum seal to a side portion of a sputtering reactor and tosupport said target thereupon.
 23. The target of claim 22, wherein saidannular projection is configured to form one side of a plasma dark spaceagainst said side portion of said sputtering reactor.
 24. The target ofclaim 16, wherein said projection is rounded in a radial direction withrespect to said central axis.
 25. The target of claim 16, whereinannular flange is integral with said outer sidewall.
 26. A target foruse in a sputter reactor having a magnetron being at least partiallyrotatable about a central axis, comprising a vault-shaped continuousmember having a vault annular about said central axis with a width of atleast 7 cm and disposed on a first side of said target facing aninterior of said reactor and having an annular inner sidewall, anopposed annular outer sidewall, a top wall, and an annular flangeextending radially outwardly from said outer sidewall configured to besupported on said reactor, an aspect ratio of a depth of said vault to awidth of said vault being at least 1:2, said target being continuouswithin said vault and in an area radially inwardly of said innersidewall.
 27. The target of claim 26, wherein said continuous memberadditionally comprises a planar face wall attached to said first side ofsaid inner sidewall.
 28. The target of claim 27, wherein a well isformed by said inner sidewall and said planar face wall able toaccommodate a portion of said magnetron adjacent said inner sidewall.29. The target of claim 26, wherein said aspect ratio is at least 1:1.30. The target of claim 26, wherein said continuous member is formed ofcopper.
 31. The target of claim 26, wherein said annular flange isadapted to support said target on said sputter reactor.
 32. The targetof claim 31, further comprising an annular projection extending awayfrom said flange in an area of said outer sidewall and configured toform a plasma dark between it and a side portion of said sputterreactor.
 33. A sputtering target adapted for use in a magnetron sputterreactor designed to sputter material of said target onto a wafer havinga maximum diameter and comprising a continuous member having a vaultannular about a central axis and disposed on a first side of said targethaving an annular inner sidewall, an opposed annular outer sidewall of adiameter greater than said maximum diameter of said wafer, a top wall,and an annular flange extending radially outwardly from said outersidewall, an aspect ratio of a depth of said vault to a width of saidvault being at least 1:2, said target being continuous within said vaultand in an area radially inwardly of said inner sidewall.
 34. Thesputtering target of claim 33, wherein said aspect ratio is at least1:1.
 35. The sputtering target of claim 33, wherein a width of saidvault is at least 5 cm.
 36. The sputtering target of claim 33, which isa copper target.
 37. The target of claim 33, wherein said annular flangeis adapted to vacuum seal to a chamber sidewall of a sputtering reactorand to support said target thereupon.
 38. A plasma sputter reactor,comprising: a chamber wall; a pedestal for supporting a substrate to besputter coated; an isolator supported on said chamber wall; a metalshield protecting said isolator and said chamber wall from being sputtercoated; and a target supported on said isolator and comprising acontinuous vault-shaped member having a vault annular about a centralaxis and disposed on a first side of said target having an annular innersidewall, an opposed annular outer sidewall, a top wall, an annularflange extending radially outwardly from said outer sidewall andsupported on said isolator, and an annular projection extending awayfrom said flange in an area of said outer sidewall and forming a plasmadark space in opposition to said shield, an aspect ratio of a depth ofsaid vault to a width of said vault being at least 1:2.
 39. The reactorof claim 38, wherein said aspect ratio is at least 1:1.
 40. The reactorof claim 38, wherein a width of said vault is at least 5 cm.
 41. Thereactor of claim 38, wherein said target is a copper target.
 42. Thereactor of claim 38, wherein a diameter of said outer sidewall isgreater than a diameter of said pedestal.
 43. A sputter target adaptedfor use with a magnetron sputter reactor, being composed substantiallyof a material to be sputtered, and being shaped to have an annular vaulton a first side having an aspect ratio of at least 1:2 and surrounding acentral axis, a well on a second side of said target surrounded by andseparated from said vault by an inner sidewall, an outer sidewallforming a radially outermost portion of said vault, a roof connectingsaid inner and outer sidewalls, an outer flange extending radiallyoutwardly from an end of said outer sidewall opposite said roof forbeing sealed to a vacuum chamber of said reactor, and a cylindrical knobextending from a juncture of said flange and said outer sidewall awayfrom said roof, a plasma dark space being formable between said knob andsaid vacuum chamber.
 44. The target of claim 43, wherein said aspectratio is at least 1:1.
 45. The target of claim 43, wherein said materialis copper or a copper alloy consisting of copper and less than 10% of analloying element.
 46. The target of claim 43, wherein said knob isrounded in a radial direction with respect to said central axis.